The objective of this proposal on the regulation of membrane phospholipid synthesis is the selection, biochemical, and genetical characterization of mutants of Escherichia coli defective in membrane phospholipid synthesis. Using plsB mutants conditionally defective in phospholipid synthesis, conditions will be established to supplement the cells with phospholipid and/or intermediates of phospholipid synthesis. Studies on the uptake of intact phospholipids will provide basic information on membrane fusion and allow modification of the composition of polar head groups of the membrane lipid. Mutants defective in phospholipid biosynthesis will be selected in the basis of auxotrophic requirements. The availability of these mutants will allow studies on the modification of membrane lipid composition, on membrane biogenesis, and on the regulation of membrane protein synthesis and assembly to be performed. These studies promise a better understanding of the significance of the diversity of polar head groups, of how membranes are synthesized and assembled, and of the coordination of macromolecular synthesis with phospholipid synthesis and cell division. Enzymological studies on the biosynthetic glycerol-P dehydrogenase, glycerol-P acyltransferase, 1-acylglycerol-P acyltransferase, and phosphatidylglycerol-P synthetase in parental and mutant strains will be performed. These studies on the regulation of lipid synthesis appear to be of significance to several important human pathologies, cancer, atherosclerosis, and obesity, and should provide basic information about the role of phospholipids in the structure and function of biological membranes.